A single line-to-ground fault is the most frequently happening problem in a transmission line. Statistically, a single line-to-ground fault accounts for about 70% or more of problems happening in an extra high voltage transmission line, and in an ultrahigh voltage transmission line having wider line spacing and having a voltage of about 200 kV or higher, single line-to-ground fault accounts for about 90% or more of problems since other problems such as a line-to-line fault, double line-to-ground fault and three phase fault occur relatively less frequently.
Since most of the problems are passing problems mainly caused by natural environment, in case of a transient fault (direct lightning or induced lightning), line-to-line fault, it is very important to perform reclosing for preventing a stop of supplying power.
Typically, in a conventional reclosing method applied to domestic transmission lines, after certain predetermined dead time, a circuit breaker is automatically reclosed. An automatic reclosing method includes a three-phase auto reclosing method, a single phase auto reclosing method, and a multi-phase (single phase+three-phase) auto reclosing method.
In the three-phase auto reclosing method, in case of a fault in a transmission line, a three-phase circuit breaker is opened and reclosed. In the single phase auto reclosing method, in case of a single line-to-ground fault, only a phase having the fault is opened and reclosed. In the multi-phase auto reclosing method, in case of a single line-to-ground fault, only a phase having the fault is opened and reclosed and in case of a fault in a multi-phase circuit breaker, a three-phase circuit breaker is opened and reclosed.
However, since a conventional auto reclosing method has a certain dead time, even after an arc is extinguished, there may be an unnecessary dead time and even if faults are not completely removed, a reclosing operation may be performed. Further, a reclosing operation may be performed even in case of a permanent fault, there may threatena power system stability and be a serious loss in power equipment.
Therefore, limitations of the conventional auto reclosing method need to be improved to perform an auto reclosing operation more efficiently.